The Missouri Supreme Court on Tuesday denied a motion from attorneys seeking to halt the execution of a man scheduled to die next week but did not explain its decision.

Attorneys for Marcellus Williams had asked the state Supreme Court and Gov. Eric Greitens to stop the punishment, citing DNA evidence that they say exonerates him. Williams, 48, is scheduled to die by injection Aug. 22 for fatally stabbing former St. Louis Post-Dispatch reporter Lisha Gayle in 1998 during a robbery at her University City home.

In a filing to the Missouri Supreme Court and a clemency request to the Republican governor, Williams' attorneys said testing conducted in December using techniques that were not available at the time of the killing shows DNA found on the knife matches an unknown man, but not Williams.

"That means in our mind the actual killer is not him," one of Williams' lawyers, Kent Gipson, told The Associated Press in a phone interview Tuesday ahead of the court's decision. "It certainly would give most reasonable people pause to say, 'Should you be executing somebody when you've got reasonable evidence suggesting another man did it?'"

After the ruling, Gipson told St. Louis Public Radio that he was surprised by the quick decision and planned to appeal to the U.S. Supreme Court.

"Certainly something involving a claim of innocence that is this substantial, you would think they would at least write an opinion or at least a short opinion giving the reasons why they denied it," Gipson said, "because that makes it more difficult to take it up to a higher court because they don't know exactly on what basis the ruling was made."

Loree Anne Paradise, a spokeswoman for Attorney General Josh Hawley, said the office remains confident that Williams is guilty based on other evidence in the case. Greitens' spokesman, Parker Briden, declined comment, saying only that the claim will need further review.